Chiral rhodium-diphosphine complexes and their use in asymmetric hydrogenations are already known from the literature. Usually, these complexes are cationic or contain--when they are neutral--chlorine, bromine or iodine as the ligand X. The optical yields which are obtained with the use of such complexes in asymmetric hydrogenations lie in the most favourable cases at about 80-84% in the case of the hydrogenation of ketopanto-lactone.